Method for controlling ink characteristics

ABSTRACT

In the operation of an ink jet printing system which recycles unused ink, changes in the formulation of the ink being used for printing which can cause deterioration of printing, is avoided by an arrangement for sensing the amount of ink in an ink reservoir and replenishing it when below a predetermined level, with a solvent-ink mixture which restores the ink in the reservoir to a proper formulation.

Umted States Patent 1191 1111 3,835,881 Dal et al. Sept. 17, 1974 [54] METHOD FOR CONTROLLING INK 3,437,107 4/1969 Wasclcski, Jr. 137 392 CHARACTERISTICS ginncgan ranton Inventors: g g y r 2 gg g p g 3,537,472 11/1970 1111110 137/392 0 er eur, 1es, o o [73 Assignee: A. B. Dick Company, Chicago, 111. Primary Examiner-William Cline Asslstant Examiner-Dawd R. Matthews 1 1 Flledi 1 1972 Attorney, Agent, or FirmLindenberg, Freilich, [21] Appl 319,852 Wasserman, Rosen & Fernandez [52] US. Cl. 137/389, 137/392 [57] 51 1111.0. Fl6k 31/02 the operano". Of mk Prmmg f' whmh [58] Field of Search 137/386, 389 392 393; recycles unused mk, changes 1n the formulation of the ink being used for printing which can cause deterioration of printing, is avoided by an arrangement for [56] References Cited sensing the amount of ink in an ink reservoir and replenishing it when below a predetermined level, with :1 UNITED STATES PATENTS solvent-ink mixture which restores the ink in the reser- 2,399,688 5/1946 Metzner Ct :11 137/386 x to a proper f l ti 2,578,921 12/1951 Cramer 3,288,061 11/1966 Doyle 101/366 X 6 Claims, 2 Drawing Figures NOZZLE VALVE 52 CONTROL 2 )4 CJRCU 1T PUMP ta Z 5O 26 CATCHER 18 l I 1 ,22 l I I-I-E L j: 1.; r LEVEL i i PUMP SOLVENT QETECYOR L I 1 \N K i =-1 MlXT i i 1 N K 1 10 11 {1 LI U BACKGROUND OF THE INVENTION This invention relates to ink drop printers and, more particularly, to an arrangement for preventing the quality of the printing from deteriorating.

Ink drop printers are well known, being described for example, in US. Pat. No. 2,5 12,743. Ari ink drop printing system usually comprises an ink reservoir, where ink under pressure is supplied to a nozzle. A transducer is usually employed, which squeezes or vibrates the nozzle at a frequency determined by an oscillator. An ink stream is emitted from the nozzle for a short distance at which point, ink drops are formed. Around the region where the ink drops are formed, a charging ring is applied. Voltages are applied to the ring, which in turn, charge the drops being formed so that each drop, as it continues on its path toward a receiving paper, will bear a charge. Each drop passes between two electrodes across which an electric field is established, so that the drop is deflected in accordance with the charge thereon, as it passes through this electric field. The drop finally impacts on paper to form a character or code marking, as determined by the video signals being used for charging the drops. Drops which are not used in printing are usually caught at a location adjacent the paper and, are returned to the reservoir for reuse.

In the operation of this ink drop printing system, some evaporation of the solvent from the ink mixture, occurs which changes the characteristics of the ink. These changing characteristics affect the drop formation, consequently; the quality of jet printing. Heretofore, this has required that the ink be replaced with fresh ink.

OBJECTS AND SUMMARY OF THE INVENTION An object of this invention is to provide a method and means for maintaining the solvent-ink mixture within a predetermined range.

Another object of this invention is to eliminate changing characteristics in ink drop formation caused by loss of solvent from the ink mixture being used.

Still another object of the invention is the provision of an improvement in an ink printing system for maintaining the quality of the ink drop printing.

These and other objects of the invention are achieved by sensing the level of the solvent-ink mixture in the ink reservoir, and when this drops to a predetermined value, provision is made for detecting this, and enabling a predetermined amount of a solvent-ink mixture to be added to the ink in the ink reservoir to bring back the solvent-ink mixture to a desired formulation, and thereby to provide desired and proper characteristics for printing.

The novel features of the invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of an embodiment of the invention.

FIG. 2 is a schematic diagram showing the circuitry which is employed in this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, there may be seen a schematic drawing of an embodiment of this invention. A tank 10 constitutes a reservoir for a solvent-ink mixture 12 which is contained therein. A pipe 14 leads from the ink reservoir to a nozzle 16, from which an ink stream is emitted for the purpose of forming ink drops. A pump 18 applies pressure to the ink in the tank, forces it up the pipe 14, and out through the nozzle 16.

Not shown, is the arrangement which follows the nozzle, whereby the ink drops are charged and thereafter deflected in accordance with that charge to impact at a location upon paper which determines the letter or symbol-or waveform, which is to be viewed. As indicated previously, this is a well known arrangement being shown in US. Pat. No. 2,512,743, for example. Thus, it need not be repeated here. Those drops which are not charged, which, in the course of printing, may constitute a considerable number, are not thrown away, but are usually collected by a catcher, here designated as an unused ink catcher 20, and are returned from that catcher back to the reservoir to be used again.

As a result of the unused ink being exposed to the atmosphere, evaporation will occur of the solvent in the ink, thus, after a period of use, the ink proportions of the mixture in the reservoir is changed, whereby ink drop formation and characteristics, and consequently the quality of the printing is changed. The change in the ink-solvent mixture is usually such as to cause the den sity of the mixture to increase, whereby drop formation rate and drop size may change. This adversely affects the printing. This has required heretofore, that the ink in the reservoir be removed and replaced with a fresh mixture.

In accordance with this invention, means are provided for bringing the ink mixture in the ink reservoir back to a desired composition, wherein its properties and behavior in use in the ink drop printing system are predictable and acceptable.

In accordance with this invention, as may be seen in FIG. 1, a level detector 22 senses when the ink in the reservoir drops to a predetermined value. At this time, the level detector provides a signal to a valve control circuit 24. The valve control circuit enables a valve 26 to open for a predetermined interval to enable a solvent-ink mixture to flow from a tank 28, wherein it is contained through a pipe 30, into the tank l0. The solvent-ink mixture flowing from the tank 28 is proportioned to bring the ink mixture 12 in the tank 10, back to the desired formulation when a predetermined amount of the solvent-ink mixture from the tank 28 has been added thereto. A pump 32 maintains pressure on the surface of the solvent-ink mixture in the tank 28 so that when the valve 26 is opened, the ink will flow through pipe 30 into the tank 10.

FIG. 2 is a block schematic diagram of a level detecting and valve control circuit, in accordance with this invention. A thermistor 40 is inserted into the reservoir 10, at a level at which it is determined that a fresh amount of solvent-ink mixture should be added. The temperature of the thermistor is lower when it is immersed in the ink mixture, which acts as a coolant, than where it is no longer so immersed. The thermistors resistance varies inversely with its temperature. A differresistance attains a predetermined value, indicative of the fact that it is no longer immersed in the ink mixture,

an output is provided by the differential amplifier 42.

The differential amplifier output is applied to an amplifier 45 which drives a time delay circuit 46. The time delay circuit 46 operates a solenoid 48, which opens the valve 26. The time delay circuit maintains the solenoid operative and thus, the valve open for a predetermined interval. This interval is determined by the amount of solvent-ink mixture desired to be added and the length of time required for this amount to be transferred into the reservoir. The thermistor 40 is cooled below the temperature at which its resistance is such that the differential amplifier can provide an output by the added solvent-ink mixture. Thus, at the end of the period for adding additional solvent ink mixture, the system is ready for a new cycle of operation.

There has accordingly been described herein a novel and useful system for maintaining the ink formulation substantially constant in an ink recycling ink drop printing system, and thereby maintaining the quality of the printing constant.

What is claimed is:

1. In an ink recycling, ink drop writing system of the type wherein a first reservoir provides a solvent-ink mixture which is formed into drops which are projected toward a writing medium, some of said drops being used for writing and the remainder being returned to said first reservoir,

means for maintaining the proportions of the solventink mixture in said first reservoir substantially constant comprising:

a second reservoir for a solvent-ink mixture,

pipe means coupling said second reservoir to said first reservoir for transferring solvent-ink mixture to said first reservoir,

inoperative valve means in said pipe means for preventing transfer of solvent-ink mixture between said second reservoir and said first reservoir until rendered operative,

level detector means in said first reservoir for provid ing an indication when the level of the ink therein falls below a predetermined level, and

time delay means responsive to said indication for rendering said inoperative valve means operative for a predetermined interval whereby a predetermined amount of solvent-ink mixture is transferred to said first reservoir to restore the proportions of said solvent-ink mixture to said substantially constant proportions.

2. In an ink recycling, ink drop system as recited in claim 1 wherein said level detector means comprises:

means having a first temperature when immersed in said solvent-ink mixture and a second temperature when not immersed in said solvent-ink mixture.

3. In an ink recycling, ink drop system as recited in claim 2 wherein said level detector means comprises:

a thermistor.

4. In an ink recycling, ink drop writing system of the type wherein a first reservoir provides a solvent-ink mixture which is formed into drops which are projected toward a writing medium, some of said drops being used for writing and the remainder being returned to said first reservoir,

means for maintaining the solvent-ink formulation in said first reservoir substantially constant comprising:

a second reservoir for a solvent-ink mixture,

pipe means coupling said second reservoir to said first reservoir for transferring solvent-ink mixture to said first reservoir,

inoperative valve means in said pipe means for preventing transfer of solvent-ink mixture between said second reservoir and said first reservoir until rendered operative,

thermistor sensing means in said ink reservoir having a first resistance value when it is not immersed in said solvent-ink mixture and a second resistance value when it is immersed in said solvent-ink mixture,

means responsive to said first resistance value for producing an output signal indicative thereof, and

time delay circuit means responsive to said output signal for rendering said inoperative valve means operative for a predetermined interval whereby a predetermined amount of solvent-ink mixture is transferred to'said first reservoir to restore the formulation of the solvent ink therein to said substantial constant formulation.

5. In an ink recycling ink drop writing system of the type wherein the solvent-ink mixture in a reservoir is formed into drops which are projected toward a writing medium, some of said drops being used for writing and the remainder being returned to said solvent-ink mixture reservoir, the method of maintaining the proportions of the solvent-ink mixture substantially constant comprising placing a thermistor means a predetermined distance below the level in said reservoir of the solvent-ink mixture having desired proportions,

deriving an output signal from said thermistor when the level of said solvent-ink mixture drops to expose said therrnistor means,

adding a predetermined amount of a solvent-ink mixture to said reservoir responsive to said output signal to maintain the proportions of said solvent-ink mixture substantially constant.

6. In an ink recycling ink drop writing system as recited in claim 5 wherein said step of adding a predetermined amount of a solvent-ink mixture to said reservoir responsive to said output signals comprises opening a flow control valve, in a pipe which couples an auxiliary reservoir of a solvent-ink mixture to said reservoir, for a predetermined interval to enable the transfer of a predetermined amount of inksolvent mixture from said auxiliary reservoir to said reservoir.

JI'QJNITED STATES PATENT OFiICE 'T CERTIFICATE OF CORRECTION p 3 Dated September 17, 1974 Henry Dahl et a1.

Inventofls) It is certified that error appears in the above-identified patentand that said Lie tte rs Patent are'hereby corrected as shown below:

The name' of the Patentee should read Her try A. Dahl Signed and sealed this 5th day of November 1974.

(SEAL) Attest:

McCOY M. GIBSON-JR. C. MARSHALL DANN Attesting Officer; commissioner of Patents FORM po-wsouo-es) v v ceo31e-P69 A EUNITED STATES PATENT OFfICE CERTIFICATE OF CORRECTION-'- patent n 3835,831 Dated September 17, 1974 Henry Dahl et 211.

Inventor(s) It is certified that error appears in the above-iciefltified patent" and that said Lette z s Patent arehereby corrected as shown below:

The nameiof the Patentee should read A. Deinl' Signed and-sealed this 5th day of November 1974.

(SEAL) Attest:

MCCOY GIBSON' JR. c. MARSHALL .DANN Attestin'g Officer" Commissioner of Patents FORM Po-mso (10-69) o USCOMM-DC 60376-P69 uoso covijnmzm mnmue OFFICE: 9 O 

1. In an ink recycling, ink drop writing system of the type wherein a first reservoir provides a solvent-ink mixture which is formed into drops which are projected toward a writing medium, some of said drops being used for writing and the remainder being returned to said first reservoir, means for maintaining the proportions of the solvent-ink mixture in said first reservoir substantially constant comprising: a second reservoir for a solvent-ink mixture, pipe means coupling said second reservoir to said first reservoir for transferring solvent-ink mixture to said first reservoir, inoperative valve means in said pipe means for preventing transfer of solvent-ink mixture between said second reservoir and said first reservoir until rendered operative, level detector means in said first reservoir for providing an indication when the level of the ink therein falls below a predetermined level, and time delay means responsive to said indication for rendering said inoperative valve means operative for a predetermined interval whereby a predetermined amount of solvent-ink mixture is transferred to said first reservoir to restore the proportions of said solvent-ink mixture to said substantially constant proportions.
 2. In an ink recycling, ink drop system as recited in claim 1 wherein said level detector means comprises: means having a first temperature when immersed in said solvent-ink mixture and a second temperature when not immersed in said solvent-ink mixture.
 3. In an ink recycling, ink drop system as recited in claim 2 wherein said level detector means comprises: a thermistor.
 4. In an ink recycling, ink drop writing system of the type wherein a first reservoir provides a solvent-ink mixture which is formed into drops which are projected toward a writing medium, some of said drops being used for writing and the remainder being returned to said first reservoir, means for maintaining the solvent-ink formulation in said first reservoir substantially constant comprising: a second reservoir for a solvent-ink mixture, pipe means coupling said second reservoir to said first reservoir for transferring solvent-ink mixture to said first reservoir, inoperative valve means in said pipe means for preventing transfer of solvent-ink mixture between said second reservoir and said first reservoir until rendered operative, thermistor sensing means in said ink reservoir having a first resistance value when it is not immersed in said solvent-ink mixture and a second resistance value when it is immersed in said solvent-ink mixture, means responsive to said first resistance value for producing an output signal indicative thereof, and time delay circuit means responsive to said output signal for rendering said inoperative valve means operative for a predetermined interval whereby a predetermined amount of solvent-ink mixture is transferred to said first reservoir to restore the formulation of the solvent ink therein to said substantial constant formulation.
 5. In an ink recycling ink drop wRiting system of the type wherein the solvent-ink mixture in a reservoir is formed into drops which are projected toward a writing medium, some of said drops being used for writing and the remainder being returned to said solvent-ink mixture reservoir, the method of maintaining the proportions of the solvent-ink mixture substantially constant comprising placing a thermistor means a predetermined distance below the level in said reservoir of the solvent-ink mixture having desired proportions, deriving an output signal from said thermistor when the level of said solvent-ink mixture drops to expose said thermistor means, adding a predetermined amount of a solvent-ink mixture to said reservoir responsive to said output signal to maintain the proportions of said solvent-ink mixture substantially constant.
 6. In an ink recycling ink drop writing system as recited in claim 5 wherein said step of adding a predetermined amount of a solvent-ink mixture to said reservoir responsive to said output signals comprises opening a flow control valve, in a pipe which couples an auxiliary reservoir of a solvent-ink mixture to said reservoir, for a predetermined interval to enable the transfer of a predetermined amount of ink-solvent mixture from said auxiliary reservoir to said reservoir. 